Retractable zoom lens having a variable aperture-stop mechanism

ABSTRACT

A zoom lens includes a variable aperture-stop mechanism positioned in front or behind an aperture-control lens group; a first rotation imparting member, which rotates an opening/closing ring of the variable aperture-stop mechanism by a relative movement between the variable aperture-stop mechanism and the first rotation imparting member in the optical axis direction so as to hold an adjustable aperture of the variable aperture-stop mechanism at a small aperture size when the aperture-control lens group moves within in the zooming range; and a second rotation imparting member, which rotates the opening/closing ring by a relative movement between the variable aperture-stop mechanism and the second rotation imparting member to open and hold the adjustable aperture at a large aperture size when the aperture-control lens group moves to the accommodated position, at which the aperture-control lens group is partly positioned in the adjustable aperture held at the large aperture size.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a retractable zoom lens having avariable aperture-stop mechanism for varying a full-aperture F-number inaccordance with the focal length of the zoom lens.

2. Description of the Related Art

In zoom lenses (zoom lens barrels) for compact cameras which include alens shutter, specifically in such zoom lenses with a high zoom ratio,the maximum aperture size is varied in accordance with variations in thefocal length of the zoom lens since harmful rays of light need to beshut out at the wide-angle extremity and the full-aperture F-number(full-aperture F value) needs to be reduced at the telephoto extremity.

Variable aperture-stop mechanisms for making the aperture sizeadjustable are generally thick (large in size) in the optical axisdirection, which is conventionally an obstacle to reduction in length ofa retractable type of lens in its fully retracted state (accommodatedstate). In addition, although a multi-function diaphragm controlmechanism that is a combination of a shutter and a variable aperturestop is known in the art, both the mechanical structure and theelectrical control system of such a multi-function diaphragm controlmechanism are complicated because each of the shutter and the variableaperture stop needs to be controlled with precision. Accordingly, it iscostly to adopt such a multi-function diaphragm control mechanism.

SUMMARY OF THE INVENTION

The present invention provides a retractable zoom lens having a variableaperture-stop mechanism which makes it possible to perform anaperture-size varying operation (aperture-size increasing/reducingoperation) when the zoom lens is in the zooming range and anaperture-size varying operation (aperture-size increasing operation)when the zoom lens is accommodated, without increasing size of thevariable aperture-stop mechanism (specifically the length thereof in theoptical axis direction) nor complicating the structure of the variableaperture-stop mechanism.

According to an aspect of the present invention, a zoom lens isprovided, including a zoom optical system including movable lens groupsfor zooming which are moved between a ready-to-photograph position in azooming range and an accommodated position behind theready-to-photograph position in an optical axis direction, one of themovable lens groups serving as an aperture-control lens group; avariable aperture-stop mechanism which is positioned one of in front ofand behind the aperture-control lens group and is movable relative tothe aperture-control lens group in the optical axis direction, thevariable aperture-stop mechanism including a plurality of apertureblades, a base member which supports the plurality of aperture blades soas to allow each of the plurality of aperture blades to rotate freely,and an opening/closing ring which rotates relative to the base member,forward and reverse rotations of the opening/closing ring causing theplurality of aperture blades to rotate to thereby vary a size of anadjustable aperture formed by the plurality of aperture blades; a firstrotation imparting member, which rotates the opening/closing ring by arelative movement between the variable aperture-stop mechanism and thefirst rotation imparting member in the optical axis direction so as tohold the adjustable aperture at a small aperture size when theaperture-control lens group moves in the optical axis direction betweena wide-angle extremity position thereof and a position in a vicinity ofthe wide-angle extremity position in the zooming range; and a secondrotation imparting member, which rotates the opening/closing ring by arelative movement between the variable aperture-stop mechanism and thesecond rotation imparting member in the optical axis direction so as toopen and hold the adjustable aperture at a large aperture size when theaperture-control lens group moves in the optical axis direction from thewide-angle extremity position in the optical axis direction to theaccommodated position. The aperture-control lens group is partlypositioned in the adjustable aperture held at the large aperture sizewhen the aperture-control lens group is positioned in the accommodatedposition.

It is desirable for the first rotation imparting member to impart arotational force onto the opening/closing ring via another rotatingring, and for the second rotation imparting member to impart arotational force directly onto the opening/closing ring.

It is desirable for the another rotating ring to be connected with theopening/closing ring via a spring in a manner to rotate theopening/closing ring together with the another rotating ring when arotational motion is imparted onto the another rotating ring, and toallow the opening/closing ring to solely rotate when a rotational forceis imparted onto the opening/closing ring.

It is desirable for each aperture blade of the plurality of apertureblades to be biased to rotate in a direction to open the adjustableaperture.

It is desirable for the zoom lens to include a cam ring which moves themovable lens groups in the optical axis direction by forward and reverserotations of the cam ring, wherein one and the other of the forward andreverse rotations of the cam ring cause each of the movable lens groupsto move from the accommodated position to a telephoto extremity positionvia a wide-angle extremity position and from the telephoto extremityposition to the accommodated position via the wide-angle extremityposition, respectively.

It is desirable for the aperture-control lens group and the variableaperture-stop mechanism to be supported by a single moving frame.

It is desirable for the first rotation imparting member to guide thesingle moving frame linearly in the optical axis direction.

It is desirable for the opening/closing ring to include a radialprojection, and for the first rotation imparting member to include atleast one linear guide bar, which guides the single moving framelinearly in the optical axis direction; a rotation control groove, inwhich the radial projection of the opening/closing ring is engaged,being formed on the linear guide bar to control rotational position ofthe opening/closing ring.

It is desirable for the second rotation imparting member to bepositioned in front of the variable aperture-stop mechanism, and for thesecond rotation imparting member to linearly move toward and away fromthe opening/closing ring in the optical axis direction when the each ofthe movable lens groups is moved between the ready-to-photographposition in the zooming range and the accommodated position.

It is desirable for the opening/closing ring to include at least oneprojection. The second rotation imparting member includes at least onefirst surface which extends in the optical axis direction, and at leastone second surface which extends obliquely with respect to both theoptical axis direction and a circumferential direction of the secondrotation imparting member. The first surface and the second surfacerespectively come into sliding contact with the projection of theopening/closing ring to control a rotational position of theopening/closing ring when the each of the movable lens groups is movedto the accommodated position.

It is desirable for the single moving frame to move in the optical axisdirection when a zooming operation is performed.

It is desirable for the aperture-control lens group to be positionedbetween a frontmost lens group and a rearmost lens group of the movablelens groups.

According to the present invention, in a retractable zoom lens in whichthe variable aperture-stop mechanism varies (increases/reduces) theaperture size thereof when the zoom lens is in the zooming range and inwhich the variable aperture-stop mechanism increases the aperture sizethereof to make a movable lens group of the zoom lens partly positionedin the aperture of the variable aperture-stop mechanism when the zoomlens is in the accommodated position, the aperture size of the variableaperture-stop mechanism is varied from a large size to a small size (orfrom a small size to a large size) by rotating the opening/closing ringof the variable aperture-stop mechanism via either the first rotationimparting member when the zoom lens is in the zooming range or thesecond rotating imparting member when the zoom lens is accommodated.This structure improves the degree of freedom in design and neitherbrings about an increase in size of the variable aperture-stop mechanism(especially the length thereof in the optical axis direction) norcomplicates the structure of the variable aperture-stop mechanism.

The present disclosure relates to subject matter contained in JapanesePatent Application No. 2009-154729 (filed on Jun. 30, 2009) which isexpressly incorporated herein by reference in its entirety.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be described below in detail with referenceto the accompanying drawings in which:

FIG. 1 is a cross sectional view of an embodiment of a zoom lens barrelof a compact digital camera according to the present invention in aready-to-photograph state within the zooming range (more specifically,the upper half and the lower half of the zoom lens barrel show the zoomlens barrel set at the wide-angle extremity and the telephoto extremity,respectively);

FIG. 2 is a cross sectional view of the zoom lens barrel in a lensbarrel accommodated state (fully retracted state);

FIG. 3 is an exploded front perspective view of elements of the zoomlens barrel;

FIG. 4 is an exploded front perspective view of elements of the zoomlens barrel;

FIG. 5 is an exploded front perspective view of elements of the zoomlens barrel;

FIG. 6 is an exploded front perspective view of elements of the zoomlens barrel;

FIG. 7 is an exploded front perspective view of elements of the zoomlens barrel;

FIGS. 8A, 8B, 8C and 8D are front perspective views of elementsassociated with a variable aperture-stop mechanism incorporated in thezoom lens barrel, showing different operational states of the variableaperture-stop mechanism;

FIGS. 9A and 9B are rear elevational views of the variable aperture-stopmechanism, showing different operational states thereof;

FIG. 10 is a rear elevational view of an aperture blade (shown by solidor two-dot chain lines) and a fixed circular aperture (shown by atwo-dot chain line), illustrating variations in aperture size of thevariable aperture-stop mechanism;

FIG. 11 is an exploded front perspective view of elements of the zoomlens barrel that include a second lens group moving frame, the variableaperture-stop mechanism (variable aperture stop sub-assembly), aretaining ring and an inter-lens-group biasing spring;

FIGS. 12A, 12B and 12C are front perspective views of the second lensgroup moving frame, the variable aperture stop sub-assembly and theretaining ring that are shown in FIG. 11, wherein FIG. 12A shows a statewhere the variable aperture stop sub-assembly has been inserted into thesecond lens group moving frame but the retaining ring is not yetinserted into the second lens group moving frame following the insertionof the variable aperture stop sub-assembly, FIG. 12B shows a state whereboth the variable aperture stop sub-assembly and the retaining ring havebeen inserted into the second lens group moving frame but the retainingring is not yet rotated to the lock position thereof, and FIG. 12C showsa state where both the variable aperture stop sub-assembly and theretaining ring have been inserted into the second lens group movingframe and the retaining ring has been rotated to the lock positionthereof;

FIGS. 13A, 13B, 13C, 13D and 13E are front perspective views of someelements of the zoom lens barrel, showing a sequence of operations ofthe variable aperture-stop mechanism when it moves between the telephotoextremity in the zooming range and the accommodated position via thewide-angle extremity; and

FIG. 14 is a rear perspective view of a second advancing barrel of thezoom lens barrel.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The brief description of the overall structure of an embodiment of azoom lens barrel (zoom lens) ZL according to the present invention willbe hereinafter discussed with reference to FIGS. 1 through 5. Aphotographing optical system installed in the zoom lens barrel ZL isprovided with a first lens group LG1, a second lens group LG2, a thirdlens group (focusing lens group) LG3, a low-pass filter (optical filter)25 and an image sensor 26, in that order from the object side. In thefollowing descriptions, the optical axis direction refers to a directionalong or parallel to a photographing optical axis O of thisphotographing optical system.

The low-pass filter 25 and the image sensor 26 are integrated as asingle unit that is fixed to an image sensor holder 23, and the imagesensor holder 23 is fixed to the back of a housing 22 of the zoom lensbarrel ZL.

The zoom lens barrel ZL is provided with a third lens group frame 51which holds the third lens group LG3. The third lens group frame 51 issupported by the housing 22 to be movable in the optical axis directionrelative to the housing 22. The third lens group frame 51 is driven byan AF motor 160 that is supported by the housing 22 (see FIG. 3).

As shown in FIG. 3, the zoom lens barrel ZL is provided inside thehousing 22 with a movable lens unit (cam-ring-incorporated movable unit)110 which is supported by the housing 22 to be movable in the opticalaxis direction. The zoom lens barrel ZL is provided at the front end ofthe movable lens unit 110 with a barrier unit 101 for protection of thefront surface of the first lens group LG1 from being damaged when thezoom lens barrel ZL is not in use. The zoom lens barrel ZL is providedat the front end thereof with a decorative ring 108 fixed to the frontof the barrier unit 101.

As shown in FIG. 4, the movable lens unit 110 is provided with a linearguide ring 10 (for linearly guiding the second lens group LG2), a camring 11, a cam-ring connecting ring 14 and a first advancing barrel(linear guide ring for guiding the first lens group) 13. The cam ring 11is rotated by the driving force of a zoom motor 150 (see FIG. 3). Thecam ring 11 moves in the optical axis direction while rotating duringmovement from the lens barrel accommodated state (fully-retracted state)(shown in FIG. 2) until a ready-to-photograph state (the wide-angleextremity shown in the upper half of FIG. 1). The cam ring 11 rotates ata fixed position with respect to the optical axis direction when thezoom lens barrel ZL is in the zooming range (between the wide-angleextremity shown in the upper half of FIG. 1 and the telephoto extremityshown in the lower half of FIG. 1) in a ready-to-photograph state.

The first advancing barrel 13 is positioned in front the cam ring 11(specifically, a combination of the cam ring 11 and the cam-ringconnecting ring 14) and the linear guide ring 10 is position behind thecam ring 11. Each of the linear guide ring 10 and the first advancingbarrel 13 is guided linearly in the optical axis direction with respectto the housing 22, and is connected to the cam ring 11 to be rotatablerelative to the cam ring 11 and to move with the cam ring in the opticalaxis direction.

The cam-ring connecting ring 14 is an element for connecting the firstadvancing barrel 13 and the cam ring 11 to each other (by a bayonetcoupling) so that the first advancing barrel 13 and the cam ring 11 canrotate freely relative to each other and integrally move in the opticalaxis direction.

The zoom lens barrel ZL is provided radially inside of the cam ring 11with a second lens group holding unit 80. The linear guide ring 10guides the second lens group holding unit 80 linearly in the opticalaxis direction so that the second lens group holding unit 80 can move inthe optical axis direction relative to the linear guide ring 10. Asshown in FIG. 6, the second lens group holding unit 80 is provided witha second lens group moving frame 8, and is provided inside the secondlens group moving frame 8 with a second lens group holding frame 2 whichholds the second lens group LG2. The second lens group LG2 is thesmallest in diameter among all the lens groups of the photographingoptical system. The second lens group holding unit 80 is provided, infront of and behind the second lens group holding frame 2 in the opticalaxis direction, with a variable aperture-stop mechanism 70 and a shutterunit 100, respectively, each of which is supported by the second lensgroup moving frame 8 to be movable in the optical axis directionrelative to the second lens group moving frame 8. The zoom lens barrelZL is provided, in the immediate vicinity of a set of shutter blades100S contained in the shutter unit 100, with an ND filter 90 (seeFIG. 1) for exposure control that is provided as a replacement for amechanical diaphragm mechanism. In the present embodiment of the zoomlens barrel, the second lens group LG2 that is held by the second lensgroup holding unit 80 serves as a light-quantity-control lens group.

The zoom lens barrel ZL is provided immediately inside the firstadvancing barrel 13 with a second advancing barrel 12 which advances andretracts in the optical axis direction relative to the first advancingbarrel 13. The barrier unit 101 is fixed at the front end of the secondadvancing barrel 12. The first advancing barrel 13, which is guidedlinearly in the optical axis direction with respect to the housing 22,guides the second advancing barrel 12 linearly in the optical axisdirection so that the second advancing barrel 12 can move in the opticalaxis direction relative to the first advancing barrel 13. The zoom lensbarrel ZL is provided inside the second advancing barrel 12 with a firstlens group holding frame 1 which holds the first lens group LG1 (seeFIG. 5), so that the second advancing barrel 12 supports the first lensgroup LG1 via the first lens group holding frame 1.

The second advancing barrel 12 is provided with a plurality of first camfollowers CF1 (see FIGS. 1, 2 and 5), each of which projects radiallyinwards, for moving the first lens group LG1. Each first cam followerCF1 is slidably engaged in an associated first-lens-group control camgroove CG1 formed on an outer peripheral surface of the cam ring 11.Since the second advancing barrel 12 is guided linearly in the opticalaxis direction via the first advancing barrel 13, rotation of the camring 11 causes the second advancing barrel 12 (i.e., the first lensgroup LG1) to move in the optical axis direction in a predeterminedmoving manner in accordance with the contours of the first-lens-groupcontrol cam grooves CG1.

The second lens group moving frame 8 is provided on an outer peripheralsurface thereof with a plurality of second cam followers CF2, each ofwhich projects radially outwards to be slidably engaged in an associatedsecond-lens-group control cam groove CG2 formed on an inner peripheralsurface of the cam ring 11. Since the second lens group moving frame 8is guided linearly in the optical axis direction via the linear guidering 10, rotation of the cam ring 11 causes the second lens group movingframe 8 (i.e., the second lens group LG2) to move in the optical axisdirection in a predetermined moving manner in accordance with thecontours of the second-lens-group control cam grooves CG2.

The zoom lens barrel ZL is provided between the second lens group movingframe 8 and the second advancing barrel 12 with an inter-lens-groupbiasing spring 27, in the form of a compression spring which biases thesecond lens group moving frame 8 and the second advancing barrel 12 inopposite directions away from each other.

The shutter unit 100 is provided with a guide cylinder 100 a which isformed integral with the shutter unit 100 to extend in the optical axisdirection. The second lens group moving frame 8 is provided with a pairof (front and rear) guide pins 100 b (see FIGS. 1 and 6) which areinserted into the guide cylinder 100 a from the front and the rear,respectively. The guide pin 100 b which appears in FIG. 6 is the rearguide pin 100 b which is fixed to the second lens group moving frame 8by a set screw. A compression coil spring 100 c (see FIG. 6) is fittedon the front guide pin 100 b to bias the shutter unit 100 rearward. Withthis guide mechanism, the shutter unit 100 is positioned at apredetermined position spaced farthest apart from the second lens groupmoving frame 8 in a ready-to-photograph state, and moves close to eachof the second lens group LG2 and the third lens group LG3 when the zoomlens barrel ZL is accommodated (fully retracted) (see FIGS. 1 and 2).The set of shutter blades 100S of the shutter unit 100 can be controlledto fully open and shut upon a shutter release in the zooming range andfully open in the lens barrel accommodated state.

As shown in FIG. 6, the variable aperture-stop mechanism 70 is providedwith a base member 73, an opening/closing ring 72, a set of threeaperture blades 74 and a zoom rotational ring 71. As can be clearly seenin FIGS. 9A, 9B and 10, three rotational center projections 73 b whichare fitted into three rotational center holes 74 a formed through thethree aperture blades 74 project from the base member 73, respectively.Each aperture blade 74 is provided with an opening/closing cam groove 74b so that this opening/closing cam groove 74 b and the associatedrotational center hole 74 a are formed as a pair. Three opening/closingpins 72 a project from the opening/closing ring 72 to be engaged in thethree opening/closing grooves 74 b of the set of three aperture blades74, respectively. Rotating the opening/closing ring 72 relative to thebase plate 73 causes the size of the aperture formed by the set of threeaperture blades 74 to change. Each opening/closing cam groove 74 b isprovided with an aperture closing section 74 b 1 and an aperture openingsection 74 b 2. The aperture closing section 74 b 1 has both acircumferential directional component (in the circumferential directionof the opening/closing ring 72) and a radial directional component (in aradial direction of the opening/closing ring 72), however, thecircumferential directional component is much greater than the radialdirectional component. The aperture opening section 74 b 2 has both acircumferential directional component (in the circumferential directionof the opening/closing ring 72) and a radial directional component (in aradial direction of the opening/closing ring 72), however, the radialdirectional component is much greater than the circumferentialdirectional component. When the three opening/closing pins 72 a arepositioned in the aperture opening sections 74 b 2 of the set of threeaperture blades 74, respectively, a rotation of the opening/closing ring72 at a small angle of rotation can cause the size of the apertureformed by the set of three aperture blades 74 to become maximum as shownin FIGS. 9A and 10. On the other hand, when the three opening/closingpins 72 a are positioned in the aperture closing sections 74 b 1 of theset of three aperture blades 74, respectively, the size of the apertureformed by the set of three aperture blades is maintained minimum duringrotation of the opening/closing ring 72 through a relatively large angleof rotation as shown in FIGS. 9B and 10. A large-diameter circularaperture (fixed circular aperture) 73 c (see FIG. 9A), which is smallerin diameter than the maximum size of the aperture formed by the set ofthree aperture blades 74 and greater in diameter than the minimum sizeof the aperture formed by the set of three aperture blades 74, is formedin the base member 73. In this manner, by defining the maximum size ofthe aperture of the variable aperture-stop mechanism 70 by thelarge-diameter circular aperture 73 c, not by the set of three apertureblades 74, the maximum size of the aperture of the variableaperture-stop mechanism 70 can be controlled with high precision. On theother hand, controlling the minimum aperture of the variableaperture-stop mechanism 70 through the use of the closing section 74 b 1(the circumferential component of which is much greater in magnitudethan the radial component thereof) of each opening/closing cam groove 74b makes it possible to control the size of the minimum aperture of thevariable aperture-stop mechanism 70 with high precision. Namely, asshown in the enlarged view in FIG, 10, in a state where the apertureformed by the set of three aperture blades 74 (shown by solid lines inFIGS. 9B and 10) is small in size, the three opening/closing pins 72 aare positioned in the aperture closing sections 74 b 1 of the set ofthree aperture blades 74, respectively, while a central line R1 of theaperture closing section 74 b 1 of each aperture blade 74 substantiallycoincides with a rotational moving path R2 of the axis of the associatedopening/closing pin 72 a about the rotational axis thereof (whichcorresponds to the optical axis O), and accordingly, the aperture formedby the set of three aperture blades 74 can be maintained at a correctsmall size (minimum size) even if each opening/closing pin 72 a (theopening/closing ring 72) has some degree of error in angle of rotationthereof.

Although the set of three aperture blades 74 of the variableaperture-stop mechanism 70 have the three rotational center holes 74 a,respectively, while the base member 73 has the three rotational centerprojections 73 b to correspond to the three rotational center holes 74 ain the present embodiment of the variable aperture-stop mechanism, thishole-projection relationship can be reversed. Namely, it is possiblethat three rotational center holes corresponding to the three rotationalcenter holes 74 a be formed in the base member 73 while three rotationalcenter projections corresponding to the rotational center projections 73b be formed on the set of three aperture blades 74. Likewise, althoughthe three opening/closing cam grooves 74 b are respectively formed inthe set of three aperture blades 74 while the three opening/closing pins72 a are formed on the opening/closing ring 72 in the present embodimentof the variable aperture-stop mechanism, it is possible that threeopening/closing cam grooves corresponding to the three opening/closingcam grooves 74 b be formed in the opening/closing ring 72 while threeopening/closing pins corresponding to the three opening/closing pins 72a be formed on the set of three aperture blades 74, respectively.

In short, the base member 73, the opening/closing ring 72 and the set ofthree aperture blades 74 constitute an aperture blade opening/closingmechanism, and the adjustable aperture formed by the set of threeaperture blades 74 can change between the maximum aperture and theminimum aperture by rotating the opening/closing ring 72 relative to thebase member 73. The maximum aperture size of the adjustable aperture isgreater than the diameter of the circular aperture 73 c and the minimumaperture size of the adjustable aperture is smaller than the diameter ofthe diameter of the circular aperture 73 c. In addition, the set ofthree aperture blades 74 is positioned closer to the second lens groupLG2 than the circular aperture 73 c.

The zoom rotational ring 71 of the variable aperture-stop mechanism 70prevents the opening/closing ring 72 from coming off with theopening/closing ring 72 being held between the zoom rotational ring 71and the base member 73, and is coupled to the base member 73 by bayonetcoupling in a manner to be rotatable relative to the base member 73through a predetermined angle of rotation. The variable aperture-stopmechanism 70 is provided with an extension coil spring 76 which isextended to be installed between the zoom rotational ring 71 and theopening/closing ring 72. The extension coil spring 76 makes theopening/closing ring 72 rotate with the zoom rotational ring 71 when arotational force is applied to the zoom rotational ring 71. When arotational force in a direction to open the aperture formed by the setof three aperture blades 74 is applied to the opening/closing ring 72,the extension coil spring 76 is extended to allow the opening/closingring 72 to rotate solely. In addition, the variable aperture-stopmechanism 70 is provided with an extension coil spring 77 which isextended to be installed between the zoom rotational ring 71 and thebase member 73. The extension coil spring 77 biases the zoom rotationalring 71 in a direction to open the aperture formed by the set of threeaperture blades 74.

The base member 73, the opening/closing ring 72, the set of threeaperture blades 74, the zoom rotational ring 71 and the two extensioncoil springs 76 and 77 are assembled together into a variable aperturestop sub-assembly SA as shown in FIG. 11. This variable aperture stopsub-assembly SA is inserted into the front opening of the second lensgroup moving frame 8 and held thereby via a retaining ring 75 as shownin FIGS. 11 and 12. The base member 73 is provided with a plurality ofguide projections 73 a (see FIG. 6) which project radially outwards tobe slidably engaged in a plurality of linear guide grooves 8 a,respectively, which are formed on an inner peripheral surface of thesecond lens group moving ring 8. The second lens group moving ring 8 isfurther provided with a plurality of retaining projections 8 b whichproject radially inwards from a circular cylindrical wall surface at thefront end opening of the second lens group moving ring 8. The retainingring 75 is provided with a plurality of assembling grooves 75 a arrangedin alignment with the plurality of retaining projections 8 b,respectively. The retaining ring 75 is supported by the second lensgroup moving ring 8 on an inner peripheral surface thereof at the frontend opening of the second lens group moving ring 8 through the use ofthe plurality of retaining projections 8 b and the plurality ofassembling grooves 75 a with two compression coil springs 78, forbiasing the variable aperture stop sub-assembly SA forward, beinginstalled between the base member 73 and the second lens group movingring 8. The two compression coil springs 78 are positioned symmetricallywith respect to the optical axis O. A plurality of rotation stopprojections 73 d project forward from the base member 73, and aplurality of U-shaped rotation stop grooves 75 b in which the pluralityof rotation stop projections 73 d are respectively engaged are formed onthe retaining ring 75. The plurality of rotation stop projections 73 dand the plurality of U-shaped rotation stop grooves 75 b are notrespectively aligned, as viewed in the optical axis direction, when theplurality of assembling grooves 75 a and the plurality of retainingprojections 8 b are respectively aligned, as viewed in the optical axisdirection. Namely, when the plurality of rotation stop projections 73 dand the plurality of U-shaped rotation stop grooves 75 b arerespectively aligned in the optical axis direction, the plurality ofassembling grooves 75 a and the plurality of retaining projections 8 bare not respectively aligned in the optical axis direction.

FIGS. 12A, 12B and 12C show a sequence of fitting the variable aperturestop sub-assembly SA and the retaining ring 75 into the second lensgroup moving frame 8. FIG. 12A shows a state where the variable aperturestop sub-assembly SA is fitted into the second lens group moving frame 8with the plurality of guide projections 73 a of the base member 73 beingengaged in the plurality of linear guide grooves 8 a that have endopenings at the front of the second lens group moving frame 8,respectively. FIG. 12B shows a state where the retaining ring 75 isinserted into the second lens group moving frame 8 against the biasingforce of the compression coil spring 78 with the plurality of assemblinggrooves 75 a of the retaining ring 75 being aligned with the pluralityof retaining projections 8 b of the second lens group moving frame 8 inthe optical axis direction, respectively. In this state, rotating theretaining ring 75 relative to the second lens group moving ring 8 at asmall angle of rotation causes the retaining ring 75 to be partlypositioned behind the plurality of retaining projections 8 b, thuspreventing the retaining ring 75 (the variable aperture stopsub-assembly SA) from coming off the second lens group moving ring 8.This rotation of the retaining ring 75 relative to the second lens groupmoving ring 8 further causes the plurality of rotation stop projections73 d of the base member 73 to engage with the plurality of U-shapedrotation stop grooves 75 b of the retaining ring 75, respectively, thuspreventing the retaining ring 75 from rotating. In this retained state,the retaining ring 75 (the variable aperture stop sub-assembly SA) isguided linearly in the optical axis direction relative to the secondlens group moving frame 8. The engaged state between the plurality ofrotation stop projections 73 d of the base member 73 and the pluralityof U-shaped rotation stop grooves 75 b of the retaining ring 75 isstable, and there is no possibility of the variable aperture stopsub-assembly SA coming off the second lens group moving frame 8 unlessthe retaining ring 75 is firstly pressed into the second lens groupmoving frame against the biasing force of the compression coil springs78, and subsequently rotated to bring the plurality of assemblinggrooves 75 a into alignment with the plurality of retaining projections8 b, respectively.

Although the spring forces of the inter-lens-group biasing spring 27 andthe two compression coil springs 78 are exerted on the front and therear sides of the retaining ring 75, the sum of the spring forces of thetwo compression coil springs 78 is greater than the inter-lens-groupbiasing spring 27. Accordingly, in a normal state (in aready-to-photograph state in the zooming range), in which no force inthe optical axis direction is exerted on the variable aperture stopsub-assembly SA, the retaining ring 75 (the variable aperture stopsub-assembly SA) is held at the fully advanced position (in the stateshown in FIG. 1) relative to the second lens group moving frame 8, inwhich the plurality of retaining projections 8 b and the retaining ring75 are in contact with each other. When the zoom lens barrel ZL is fullyretracted, the variable aperture stop sub-assembly SA retreats by beingpressed rearward by the second advancing barrel 12 while compressing thetwo compression coil springs 78, and the retaining ring 75 moves awayfrom the plurality of retaining projections 8 b (see FIG. 2).

The zoom rotational ring 71 is provided with a radial projection 71 a(see FIGS. 6 and 11) for controlling the rotational position of the zoomrotational ring 71. The radial projection 71 a is engaged in anddisengaged from a rotation control groove 10 b formed on an innersurface of a linear guide bar 10 a (see FIGS. 4 and 13A through 13E)which projects forward from the linear guide ring 10. The rotationcontrol groove 10 b is provided with a linear groove 10 b 1 whichextends in the optical axis direction and an inclined groove 10 b 2which extends obliquely in a direction inclined to both the optical axisdirection and the circumferential direction. When the movable lens unit110 is positioned at or in the close vicinity of the telephotoextremity, the radial projection 71 a is in a non-engaged position withrespect to the rotation control groove 10 b of the linear guide bar 10a. At this time, the zoom rotational ring 71 holds the aperture formedby the set of three aperture blades 74 at the maximum aperture (at thistime the extension coil spring 77 is in a non-extended state); inaddition, in the wide-angle range (which excludes the telephotoextremity and a zooming range in the close vicinity of the telephotoextremity), the radial projection 71 a reaches the linear groove 10 b 1from the inclined groove 10 b 2, while the zoom rotational ring 71 andthe opening/closing ring 72 are rotated by the extension coil spring 76in a direction to stop down the aperture formed by the set of threeaperture blades 74 to the minimum aperture (see FIGS. 9B, 13C and 13D).Accordingly, the linear guide ring (linear guide member) 10 serves as afirst rotation imparting member which rotates the opening/closing ring72 by rotating relative to the variable aperture-stop mechanism 70 inthe zooming range.

Similar to the zoom rotational ring 71, the opening/closing ring 72 isprovided with a set of three radial projections 72 b for controlling therotational position of the opening/closing ring 72. The second advancingbarrel 12 is provided with a set of three opening-guide surfaces 12 aand a set of three opened-state holding surfaces 12 b which arecontinuously formed with each of the opening-guide surfaces 12 a,respectively, as shown in FIG. 14. When the zoom lens barrel ZL is fullyretracted, the set of three radial projections 72 b firstly engage withthe set of three opening-guide surfaces 12 a and slide thereon andsubsequently engage with the set of three opened-state holding surfaces12 b and slide thereon, respectively, to independently rotate theopening/closing ring 72 to the maximum aperture opening positionthereof, at which the size of the aperture formed by the set of threeaperture blades 74 becomes maximum, upon the second advancing barrel 12reaching the accommodated position (fully retracted position) thereof(while extending the extension coil spring 76 without rotating the zoomrotational ring 71). FIG. 14 shows the shape of the second advancingbarrel 12, clearly showing the formation positions of the set of threeopening-guide surfaces 12 a and the set of three opened-state holdingsurfaces 12 b. Accordingly, the second advancing barrel 12 serves as asecond rotation imparting member which rotates the opening/closing ring72 by moving between the accommodated position and a ready-to-photographposition (wide-angle extremity) in the zooming range relative to thevariable aperture-stop mechanism 70. In the state shown in FIG. 8A inwhich the set of three radial projections 72 b are spaced (away) fromthe set of three opening-guide surfaces 12 a, respectively, (i.e., in astate where the zoom lens barrel ZL is in a ready-to-photograph state inthe zooming range), the extension coil spring 76 is not extended.However, when the set of three radial projections 72 b slidingly moveonto the set of three opened-state holding surfaces 12 b (as shown inFIG. 8C) after first coming into contact with and then sliding on theset of three opening-guide surfaces 12 a, respectively (as shown in FIG.8B), it can be seen from FIG. 8C that the extension coil spring 76 isextended (i.e., the opening/closing ring 72 is rotated relative to thezoom rotational ring 71).

FIGS. 13A through 13E show the functional roles of the zoom rotationalring 71 (the radial projection 71 a, which is engaged in and disengagedfrom the rotation control groove 10 b) and the opening/closing ring 72(the set of three radial projections 72 b, which are engaged with anddisengaged from the set of three opening-guide surfaces 12 a and the setof three opened-state holding surfaces 12 b). FIG. 13A shows thepositional relationship among elements of the variable aperture-stopmechanism 70 and other elements associated therewith when the zoom lensbarrel ZL is set at the telephoto extremity, FIG. 13D shows thepositional relationship among the same elements when the zoom lensbarrel ZL is set at the wide-angle extremity, and FIG. 13E shows thepositional relationship among elements of the variable aperture-stopmechanism 70 and other elements associated therewith when the zoom lensbarrel ZL is accommodated (fully retracted). FIGS. 13B and 13C show thepositional relationship among elements of the variable aperture-stopmechanism 70 and other elements associated therewith when the zoom lensbarrel ZL is at two different focal length positions (an apertureopening position and an aperture stopping-down position) in the vicinityof the telephoto extremity, respectively. In the zooming range betweenthe telephoto extremity (see FIG. 13A) and the aperture opening position(see FIG. 13B), the set of three aperture blades 74 is held at themaximum aperture since the radial projection 71 a is not engaged in therotation control groove 10 b, whereas a zooming operation of the zoomlens barrel ZL from the aperture opening position (see FIG. 13B) to theaperture stopping-down position (see FIG. 13C) causes the radialprojection 71 a to slidingly move from the inclined groove 10 b 2 to thelinear groove 10 b 1 of the rotation control groove 10 b, thus stoppingdown the aperture formed by the set of three aperture blades to theminimum aperture size. In addition, when the zoom lens barrel ZL is inthe accommodated position or positioned at the wide-angle extremity, theradial projection 71 a is positioned in the linear groove 10 b 1 of therotation control groove 10 b as can be seen in the lower halves of FIGS.13D and 13E, and the set of three aperture blades 74 are supposed to beheld at the minimum-aperture forming positions thereof solely from therelationship between the set of three aperture blades 74 and the zoomrotational ring 71. However, when the zoom lens barrel ZL is in theaccommodated position, the set of three aperture blades 74 are held atthe maximum-aperture forming positions thereof because theopening/closing ring 72 is rotated along the set of three opening-guidesurfaces 12 a of the second advancing barrel in an aperture openingdirection and held in a full-aperture state by the set of threeopened-state holding surfaces 12 b regardless of (independently of) therotational position of the zoom rotational ring 71 as shown in the upperhalves of FIGS. 13A through 13E.

As shown in FIGS. 6 and 8, the second lens group moving frame 8 isprovided, on a surface thereof which faces the variable aperture stopsub-assembly SA, with a set of three safety projections (only two ofwhich are shown in FIG. 6) 8 c, and the opening/closing ring 72 of thevariable aperture stop sub-assembly SA is provided with a set of threesafety projections 72 d (see FIG. 8) formed to correspond to the set ofthree safety projections 8 c, respectively. The set of three safetyprojections 8 c and the set of three safety projections 72 d are formedon the second lens group moving frame 8 and the opening/closing ring 72,respectively, so as to be aligned in the optical axis direction (asshown in FIG. 8A) when the opening/closing ring 72 is in asmall-aperture position thereof, and not to be aligned in the opticalaxis direction (as shown in FIG. 8C) when the opening/closing ring 72 isin a large-aperture position thereof. Namely, if the variable aperturestop sub-assembly SA retreats with the rotating operation of theopening/closing ring 72 being interfered with for some reason, the setof three safety projections 8 c and the set of three safety projections72 d which are aligned in the optical axis direction bump against(interfere with) each other to thereby prevent the variable aperturestop sub-assembly SA from further retreating. On the other hand, whenthe opening/closing ring 72 is properly rotated in an aperture openingdirection and reaches the full-aperture position, the set of threesafety projections 8 c and the set of three safety projections 72 d areout of alignment in the optical axis direction, which allows thevariable aperture stop sub-assembly SA to further retreat relative tothe opening/closing ring 72.

Operations of the zoom lens barrel ZL that has the above describedstructure will be discussed hereinafter. In the lens barrel accommodatedstate shown in FIG. 2, the length of the optical system in the opticalaxis direction (the distance from the front surface (object-sidesurface) of the first lens group LG1 to the imaging surface of the imagesensor 26) is shorter than that in a ready-to-photograph state shown inFIG. 1. In the lens barrel accommodated state, immediately after atransition signal for transition from the lens barrel accommodated stateto a ready-to-photograph state (e.g., turning ON a main switch of thecamera in which the zoom lens barrel ZL is incorporated) is input to thezoom lens barrel ZL, the zoom motor 150 is driven in the lens barreladvancing direction, which causes the cam ring 11 to advance in theoptical axis direction while rotating. The linear guide ring 10 and thefirst advancing barrel 13 linearly move with the cam ring 11. Upon thecam ring 11 being rotated, the second lens group moving frame 8, whichis guided linearly in the optical axis direction via the linear guidering 10, is moved in the optical axis direction in a predeterminedmoving manner inside the cam ring 11 due to the engagement of the secondcam followers CF2 with the second-lens-group control cam grooves CG2.Additionally, upon the cam ring 11 being rotated, the second advancingbarrel 12, which is guided linearly in the optical axis direction viathe first advancing barrel 13, is moved in the optical axis direction ina predetermined moving manner outside the cam ring 11 due to theengagement of the first cam followers CF1 with the first-lens-groupcontrol cam grooves CG1.

Namely, the amount of advancement of the first lens group LG1 from thelens barrel accommodated state is determined by the sum of the amount offorward movement of the cam ring 11 relative to the housing 22 and theamount of advancement of the second advancing barrel 12 relative to thecam ring 11, and the amount of advancement of the second lens group LG2from the lens barrel accommodated state is determined by the sum of theamount of forward movement of the cam ring 11 relative to the housing 22and the amount of advancement of the second lens group moving frame 8relative to the cam ring 11. A zooming operation is carried out bymoving the first lens group LG1 and the second lens group LG2 along thephotographing optical axis O while changing the air distancetherebetween. Upon driving the zoom motor 150 in a barrel-advancingdirection so as to advance the zoom lens barrel ZL from the lens barrelaccommodated state firstly causes the zoom lens barrel ZL to move to thewide-angle extremity shown in the upper half of the cross sectional viewin FIG. 1, and further driving the zoom motor 150 in the same directioncauses the zoom lens barrel ZL to move to the telephoto extremity shownin the lower half of the cross sectional view in FIG. 1. In the zoomingrange between the telephoto-extremity and the wide-angle extremity, thecam ring 11 rotates at a fixed position as described above, thus notmoving either forward or rearward in the optical axis direction. Notethat no picture taking operation can be performed until the zoom lensbarrel ZL reaches the wide-angle extremity from the accommodated state.

Immediately after a transition signal for transition from aready-to-photograph state to the lens barrel accommodated state (e.g.,for turning OFF the aforementioned main switch of the camera in whichthe zoom lens barrel ZL is incorporated) is input to the zoom lensbarrel ZL, the zoom motor 150 is driven in the lens barrel retractingdirection, which causes the zoom lens barrel ZL to perform a lens barrelretracting operation reverse to the above described lens barreladvancing operation.

The barrier unit 101, which is fixed at the front end of the secondadvancing barrel 12, includes a set of barrier blades (not shown) whichopens and shuts the front of the first lens group LG1. This set ofbarrier blades is shut when the zoom lens barrel ZL is in theaccommodated state, and is opened in accordance with the lens barreladvancing operation of the zoom lens barrel ZL toward aready-to-photograph position (the wide-angle extremity).

The third lens group frame 51 that supports the third lens group LG3 canbe moved forward and rearward in the optical axis direction by the AFmotor 160 independently of the above described driving operations of thefirst lens group LG1 and the second lens group LG2 that are performed bythe zoom motor 150. In addition, when the photographing optical systemof the zoom lens barrel ZL is in the zooming range from the wide-angleextremity to the telephoto extremity, the third lens group LG3 is movedin the optical axis direction to perform a focusing operation by drivingthe AF motor 160 in accordance with object distance information obtainedby a distance measuring device (not shown) provided, e.g., in the camerain which the zoom lens barrel ZL is incorporated.

The shutter unit 100 and the variable aperture-stop mechanism 70 move inthe optical axis direction and control the operation of the shutterblades 100S and the operation of the aperture blades 74, respectively,in a manner which will be discussed hereinafter while the zoom lensbarrel ZL moves between the lens barrel accommodated position and aready-to-photograph position (in the zooming range). In the zoomingrange (between the wide-angle extremity and the telephoto extremity)shown in FIG. 1, the shutter unit 100 is positioned at a rear positionspaced farthest apart from the second lens group holding frame 2 (thesecond lens group LG2) by the biasing force of the compression coilspring 100 c, while the variable aperture stop sub-assembly SA of thevariable aperture-stop mechanism 70 is held at a position where theretaining ring 75 is in contact with the back surfaces of the pluralityof retaining projections 8 b by the biasing force of the compressioncoil spring 78. At the telephoto extremity or in the vicinity thereof inthe zooming range, the set of three aperture blades 74 is opened widerthan the circular aperture 73 c of the base member 73 due to thepositional relationship between the linear guide bar 10 a and the zoomrotational ring 71, and the full-aperture F-number is determined by thecircular aperture 73 c (so that the aperture size is larger in thisstate than the aperture size at the wide-angle extremity) (see FIGS. 1and 13A and 13B). On the other hand, in a wide-angle-side focal lengthrange in the zooming range that excludes the telephoto extremity andfocal lengths in the vicinity of the telephoto extremity, the set ofthree aperture blades 74 are stopped down to limit the incidence ofharmful rays of light on the image sensor 26 due to the engagement ofthe rotation control groove 10 b (10 b 1) of the linear guide bar 10 awith the radial projection 71 a of the zoom rotational ring 71 (seeFIGS. 1 and 13C and 13D). At a time of exposure, the set of shutterblades 100S of the shutter unit 100 are opened and shut while the NDfilter 90 allows the amount of incident light which corresponds to a setF-number to pass therethrough.

Movement of the zoom lens barrel ZL to the accommodated position shownin FIG. 2 from the zooming range shown in FIG. 1 causes the shutter unit100 to come into contact with a member provided behind the shutter unit100, such as the third lens group frame 51 or the image sensor holder23, to thereupon be prevented from further moving rearward and alsocauses the second lens group moving frame 8 to approach the shutter unit100 while compressing the compression coil spring 100 c. At this time,the set of shutter blades 100S and the ND filter 90 are widely opened,and the rear part of the second lens group holding frame 2 (the secondlens group LG2), which is positioned inside of the second lens groupmoving frame 8, partly enters into the adjacent openings of the widelyopened set of shutter blades 100S and the ND filter 90 (see FIG. 2).Namely, a rear end surface of the second lens group holding frame 2 (thesecond lens group LG2) in which a plane orthogonal to the optical axis Olies is positioned behind a plane orthogonal to the optical axis O inwhich the set of shutter blades 100S lie.

Simultaneously, a rearward movement of the second advancing barrel 12causes the set of three radial projections 72 b of the variableaperture-stop mechanism 70 (the variable aperture stop sub-assembly SA)to be pressed by the set of three opening-guide surfaces 12 a and theset of three opened-state holding surfaces 12 b of the second advancingbarrel 12, respectively, which causes the opening/closing ring 72 torotate in an aperture opening direction to open the aperture formed bythe set of three aperture blades 74 to the maximum size, so that themaximum aperture thereat (full-aperture F-number) is defined by thecircular aperture 73 c of the base member 73. Additionally, the rearwardmovement of the second advancing barrel 12 causes the retaining ring 75and the variable aperture stop sub-assembly SA to be pressed rearward toapproach the second lens group LG2 while compressing the compressioncoil spring 78. In this manner, the front end of the second lens groupLG2 that is supported by the second lens group moving frame 8 enters thecircular aperture (fully-open aperture) 73 c of the variable aperturestop sub-assembly SA which moves toward the second lens group LG2 tothereby achieve a reduction in length of the zoom lens barrel ZL in theaccommodated state thereof (see FIG. 2). Namely, a plane with isorthogonal to the optical axis O and tangent to a front end surface ofthe second lens group LG2 is positioned in front of both a planeorthogonal to the optical axis O in which the circular hole 73 c liesand a plane orthogonal to the optical axis in which the set of apertureblades 74 lie.

The size of the aperture formed by the set of three aperture blades 74needs to be controlled with high precision only when the aperture isstopped down to the minimum size; in other words, the size of theaperture formed by the set of three aperture blades 74 does not need tobe precisely controlled when the aperture is fully opened (because thefull-open aperture is defined by the fixed circular aperture 73 c).Accordingly, the structure of the aperture blade opening/closingmechanism for the set of three aperture blades 74 can be simplified, andhence, can be made smaller (downsized). In addition, since the set ofthree aperture blades 74, the full-open aperture of which is greater inaperture size than the fixed circular aperture 73 c, is positionedcloser to the second lens group LG2 than the fixed circular aperture 73c, the second lens group LG2 can be made to more easily (more deeply)enter the full-open aperture of the set of three aperture blades 74 toreduce the length of the zoom lens barrel ZL in its accommodated state.

Additionally, in the above described retracting operation of the zoomlens barrel ZL toward the accommodated position, in a state where therotating operation of the opening/closing ring 72 is interfered with forsome reason, the set of three safety projections 8 c of the second lensgroup moving frame 8 and the set of three safety projections 72 d of theopening/closing ring 72 remain aligned in the optical axis direction asshown in FIG. 8B. Due to this structure, even if the variable aperturestop sub-assembly SA attempts to move rearward with the opening/closingring 72 still remaining in a small-aperture position (stopped-downposition), the set of three safety projections 8 c and the set of threesafety projections 72 d interfere with (bump against) each other tothereby prevent the stopped-down aperture formed by the set of threeaperture blades 74 of the variable aperture stop sub-assembly SA and thesecond lens group LG2 (the second lens group holding frame 2) fromaccidentally interfering with (bumping against) each other. On the otherhand, if the opening/closing ring 72 rotates properly in the apertureopening direction, the set of three safety projections 8 c and the setof three safety projections 72 d are not aligned in the optical axisdirection (i.e., the positions of the set of three safety projections 8c and the positions of the set of three safety projections 72 d deviatefrom each other in the circumferential direction). Accordingly, the rearend of the second lens group LG2 can be properly accommodated in thefully-open (widely open) aperture formed by the set of three apertureblades 74 of the variable aperture stop sub-assembly SA when the zoomlens barrel ZL is fully retracted.

As described above, strictly speaking, the second lens group holdingframe 2 partly enters an opening formed by the fully-open (widely open)shutter blades 100S of the shutter unit 100 while the second lens groupLG2 partly enters the fully-open (widely open) aperture (formed by theset of three aperture blades 74) of the variable aperture-stop mechanism70 (the variable aperture stop sub-assembly SA) in the presentembodiment of the zoom lens barrel; however, the second lens groupholding frame is an element integral with the second lens group(aperture-control lens group) LG2. Accordingly, the element which atleast partly enters both the opening formed by the fully-open shutterblades 100S of the shutter unit 100 and the fully-open aperture of thevariable aperture-stop mechanism 70 by moving integrally with the secondlens group (aperture-control lens group) LG2 when the zoom lens barrelZL is fully retracted can be said to constitute part of theaperture-control lens group.

The minimum aperture of the variable aperture-stop mechanism 70 isdefined by the set of three aperture blades while the maximum apertureof the variable aperture-stop mechanism 70 is defined by the circularaperture (fixed circular aperture) 73 c in the above describedembodiment of the variable aperture-stop mechanism 70. However, themaximum aperture of the variable aperture-stop mechanism 70 can bedefined by the set of three aperture blades 74; in such a case thecircular aperture (fixed circular aperture) 73 c is not formed in thebase member 73 (nor is formed to have a greater diameter than themaximum aperture formed by the set of three aperture blades 74).

Although the variable aperture-stop mechanism 70 and the shutter unit100 are installed in front of and behind the second lens group LG2,respectively, in the above described embodiment of the zoom lens barrel,this positional relationship can be reversed. Namely, the variableaperture-stop mechanism 70 and the shutter unit 100 can be installedbehind and in front of the second lens group LG2, respectively.

The second lens group, which is the smallest in diameter among all thethree lens groups (specifically the three lens groups having a negativepower, a positive power and a positive power, respectively, from theobject side), serves as a aperture-control lens group in the abovedescribed embodiment of the three-lens-group zoom lens; however, forinstance, in a zoom lens comprising four lens groups having a positivepower, a negative power, a positive power and a positive power,respectively, from the object side, the third lens group having thesmallest diameter can be made to serve as a aperture-control lens group.

Obvious changes may be made in the specific embodiment of the presentinvention described herein, such modifications being within the spiritand scope of the invention claimed. It is indicated that all mattercontained herein is illustrative and does not limit the scope of thepresent invention.

1. A zoom lens comprising: a zoom optical system including movable lensgroups for zooming which are moved between a ready-to-photographposition in a zooming range and an accommodated position behind saidready-to-photograph position in an optical axis direction, one of saidmovable lens groups serving as an aperture-control lens group; avariable aperture-stop mechanism which is positioned one of in front ofand behind said aperture-control lens group and is movable relative tosaid aperture-control lens group in said optical axis direction, saidvariable aperture-stop mechanism including a plurality of apertureblades, a base member which supports said plurality of aperture bladesso as to allow each of said plurality of aperture blades to rotatefreely, and an opening/closing ring which rotates relative to said basemember, forward and reverse rotations of said opening/closing ringcausing said plurality of aperture blades to rotate to thereby vary asize of an adjustable aperture formed by said plurality of apertureblades; a first rotation imparting member, which rotates saidopening/closing ring by a relative movement between said variableaperture-stop mechanism and said first rotation imparting member in saidoptical axis direction so as to hold said adjustable aperture at a smallaperture size when said aperture-control lens group moves in saidoptical axis direction between a wide-angle extremity position thereofand a position in a vicinity of said wide-angle extremity position insaid zooming range; and a second rotation imparting member, whichrotates said opening/closing ring by a relative movement between saidvariable aperture-stop mechanism and said second rotation impartingmember in said optical axis direction so as to open and hold saidadjustable aperture at a large aperture size when said aperture-controllens group moves in said optical axis direction from said wide-angleextremity position in said optical axis direction to said accommodatedposition, wherein said aperture-control lens group is partly positionedin said adjustable aperture held at said large aperture size when saidaperture-control lens group is positioned in said accommodated position.2. The zoom lens according to claim 1, wherein said first rotationimparting member imparts a rotational force onto said opening/closingring via another rotating ring, and wherein said second rotationimparting member imparts a rotational force directly onto saidopening/closing ring.
 3. The zoom lens according to claim 2, whereinsaid another rotating ring is connected with said opening/closing ringvia a spring in a manner to rotate said opening/closing ring togetherwith said another rotating ring when a rotational motion is impartedonto said another rotating ring, and to allow said opening/closing ringto solely rotate when a rotational force is imparted onto saidopening/closing ring.
 4. The zoom lens according to claim 1, whereineach aperture blade of said plurality of aperture blades is biased torotate in a direction to open said adjustable aperture.
 5. The zoom lensaccording to claim 1, further comprising a cam ring which moves saidmovable lens groups in said optical axis direction by forward andreverse rotations of said cam ring, wherein one and the other of saidforward and reverse rotations of said cam ring cause each of saidmovable lens groups to move from said accommodated position to atelephoto extremity position via a wide-angle extremity position andfrom said telephoto extremity position to said accommodated position viasaid wide-angle extremity position, respectively.
 6. The zoom lensaccording to claim 1, wherein said aperture-control lens group and saidvariable aperture-stop mechanism are supported by a single moving frame.7. The zoom lens according to claim 6, wherein said first rotationimparting member guides said single moving frame linearly in saidoptical axis direction.
 8. The zoom lens according to claim 7, whereinsaid opening/closing ring comprises a radial projection, and whereinsaid first rotation imparting member comprises at least one linear guidebar, which guides said single moving frame linearly in said optical axisdirection; a rotation control groove, in which said radial projection ofsaid opening/closing ring is engaged, being formed on said linear guidebar to control rotational position of said opening/closing ring.
 9. Thezoom lens according to claim 1, wherein said second rotation impartingmember is positioned in front of said variable aperture-stop mechanism,and wherein said second rotation imparting member linearly moves towardand away from said opening/closing ring in said optical axis directionwhen said each of said movable lens groups is moved between saidready-to-photograph position in said zooming range and said accommodatedposition.
 10. The zoom lens according to claim 9, wherein saidopening/closing ring comprises at least one projection, wherein saidsecond rotation imparting member comprises: at least one first surfacewhich extends in said optical axis direction; and at least one secondsurface which extends obliquely with respect to both said optical axisdirection and a circumferential direction of said second rotationimparting member, wherein said first surface and said second surfacerespectively come into sliding contact with said projection of saidopening/closing ring to control a rotational position of saidopening/closing ring when said each of said movable lens groups is movedto said accommodated position.
 11. The zoom lens according to claim 6,wherein said single moving frame moves in said optical axis directionwhen a zooming operation is performed.
 12. The zoom lens according toclaim 1, wherein said aperture-control lens group is positioned betweena frontmost lens group and a rearmost lens group of said movable lensgroups.